bindings-posix is a low level binding to Posix.
http://hackage.haskell.org/package/bindings-posix
It is part of bindings-* packages, and makes use of facilities
and design from package bindings-common to map the standard Posix
library as described in this page:
http://www.opengroup.org/onlinepubs/9699919799/basedefs/contents.html
The major drawback is that it bindings to the Posix instance that
runs on my computer (and probably most computers using ghc and
gcc). However, if there's interest, I can add support to various
layers of Posix if someone with knowledge of Posix helps me with
environment variables I should use to (de)activate specific
functionality.
Best,
Maurício